Welcome to the site. Always a good idea to check the date on the first post in a thread. The question in this thread was posted 14 years ago and the last reply before yours was also in 2007.If it has flat top pistons it also could be a 194. The letter F means that the engine was cast in the 6th month (June). then the day of the month, then the year. I have 194 engine with the following J27 6 so it is an October 27, 1966 production motor out of a 67 Nova. Also, important is that 250 motors weren't produced until 1966. Good luck identifying it.